Pattern development in palleal buds of botryllid ascidians: Relation between parent and its buds in their body axes.

Abstract

In order to determine how the zooid pattern (normal or reversed bilateral asymmetry) is transmitted through asexual reproduction in botryllid ascidians, the axial relationship between a zooid and its palleal buds was observed in Symplegmo reptans, Metandrocarpa uedai, Polyandrocarpa misakiensis, and P. stolonifera. The bud axes developed in harmony with the parent axes, with both normal and reversed body patterns, so that (1) when buds are given off from the right (left) side of the parent, their distal side becomes the right (left) in the future zooids (coincidence of the anteroposterior axis), (2) the free surface of the developing buds, like the parent, becomes dorsal (the coincidence of dorsoventral axis), and (3) the heart (gut loop), which is an organ representing the bilateral asymmetry, arises on the distal side of the developing buds, when the buds are derived from the side where the parent heart (gut loop) was situated (coincidence of the transverse axis). This shows that the bud develops as if it knew the position on the parent lateral wall from which it has arisen, a phenomenon referred to as the parental lateral effect.